Plasma levels of pregnancy-specific beta1-glycoprotein in normal pregnancy.

Pregnancy-specific beta-glycoprotein (PSbetaG) is a major product of the trophoblast which has only recently been identified. Like human placental lactogen, the concentration of PSbetaG in maternal blood rises throughout pregnancy until about 34 weeks, thereafter tending to remain constant until term, with only a small day-to-day variation in individuals. The circulating maternal levels of PSbetaG between 34 weeks and term are about 200 mug/ml, 20 to 30 times greater than the levels of placental lactogen, thus allowing detection and measurement of PSbetaG by relatively simple techniques. The levels of PSbetaG are above the normal range in the majority of twin pregnancies. It is suggested that PSbetaG measurements may be useful in assessing placental function and may help in the detection of multiple pregnancies at an early stage of gestation.